Tablet press design



L. P. GAJDA TABLET PRESS DESIGN Filed July 29, 1965 FIG. I

INVENTOR. LEO R GAJDA ATTORNEYS Jan. 25, 1966 xr'mw, {M FM United States Patent 3,230,905 TABLET PRESS DESIGN Leo P. Gajda, Detroit, Mich., assignor, by mesne assignments, to 'Cherry-Burrell Corporation, Cedar Rapids, Iowa, a corporation of Delaware Filed July 29, 1963, Ser. No. 298,128 6 Claims. (Cl. 107--17) This invention relates to a tablet press and more particularly to a punch design for that type of press wherein a tablet is formed from powdered material.

In a tablet press of the type under consideration, the tablet is formed in a rotating die plate having a plurality of circumferentially spaced d-ie pockets traveling with die punches which enter the pockets from the top and the bottom. The charge of powder is introduced into the die pockets from the top when the upper punch is lifted and then both punches are brought together in the die under pressure to form the tablet which is later ejected. One of the problems in connection with this type of press has been to keep the punches moving freely in the bearing supports which carry them.

Generally speaking, the punches move up and down in a vertical bushing which surrounds a cylindrical portion of the punch. In some machines where a very fine material is being handled, difiiculty is experienced because of the fact that the fine powder works its way into the clearance between the punch surface and the wall of the bearing support and ultimately the punch begins to stick and the function of the machine is impaired.

It is an object of the present invention to provide a punch construction which avoids this difiiculty of lockup due to entrapped powder. Briefly, this is accomplished by providing a construction wherein the punch is formed on its outer surface with a grooved pasageway which will carry powder away from the bearingportion of the punch as the pun-ch reciprocates and rotates in its travel around the cycle of filling, compressing, and ejection.

Other objects and features of the invention relating to details of construction and operation will be apparent in the following description and claims.

Drawings accompany the disclosure and the various views thereof may be briefly described as:

FIGURE 1, a sectional view of a tablet press showing the relationship of the parts.

FIGURE 2, a view showing the two punches in tablet forming position.

FIGURE 3, sectional view showing the shape of a groove.

FIGURE 4, a sectional view showing a modified form of groove.

FIGURE 5, a view of a punch containing the alternate form of groove.

Referring to the drawings:

In FIGURE 1, a tablet forming machine is shown having a supply hopper 10 for containing a supply of powdered material to be formed into tablets. This supply hopper deposits powder on a rotating die table 12 in a suitable way to fill die openings 14 in die rings 16- carried 'by the table. The die table is suitably mounted for rotation by a central shaft 18 in a manner well known. The rotating die table includes a punch supporting ring 20 above the die pocket, this ring containing a plurality of vertical openings 22 for receiving an upper punch.

Integral with and extending downwardly from the die ring 12 is a second punch supporting ring 24 having gear teeth 26 which may be used to drive the entire rotary mechanism and having opening 28 for the lower punch units. A grooved control cam 30 controls the upper punches and a grooved control cam 32 governs ice the position of the lower punches. An upper punch 34 has a cam head 36 for cooperating with the cam groove of element 30. The punch head 38 is formed at the lower end of the upper punch and the cylindrical surfaces of the punch between the upper and lower ends are slidably supported in cylindrical recess 40. The walls of the punch which operate in the recess 40 are formed with double helical grooves 42, 44, that is, right hand and left hand which extend the length of the bearing portion of the punch. This is preferably a groove as shown in FIGURE 3, having a curved cross-section, the tangent of the curve at the surface of the punch being substantially normal to the outer walls of the punch to create sharp corners as shown by dotted line T in the figure. The lower punch has -a similar cam follower end 46 and a head portion 48, the main body of the punch being slidable in a cylindrical recess 50 in the punch ring 24. The walls of this punch are also provided with the double helical grooves 42 and 44.

With the construction above described, any powder that may sift into the normal and necessary clearance between the punch and the punch recesses will be carried out of the recesses by the helical grooves which work the material constantly as the punches move up and down and around in the supporting cylindrical recesses. In each case, the ends of the grooves project out of the bushing recesses at the end of the stroke.

In FIGURE 5, a modified punch 52 is shown having a single helical groove 54 with a rectangular cross-section as shown particularly in FIGURE 4. Here again, the sharp corners 56 prove most effective in keeping the powder from accumulating on the punch recess walls.

It will be appreciated that since the punches are being controlled vertically by cam portions 30 and 32 that side contact with these cam portions will cause a random turning of the punches in one direction or the other, depending on where cam contact occurs. While vertical motion of the punches will contribute to the cleaning action of the walls of the punches and recesses, nevertheless, the random turning also helps to facilitate this action creating a kind of a random screwing action which also moves the powder out of the bearing surfaces.

I claim:

1. In a tablet press of the type having opposed vertically movable die punches each slidably mounted in a bearing recess of a punch supporting ring for compressing powder in a die opening, a construction for preventing the accumulation of powder on the bearing surfaces of each punch within said recess which comprises a peripheral wall on each punch having a helical groove extending longitudinally of the punch to end portions thereof so that at the extremes of the stroke of the punch the groove will project from each end of a punch hearing recess, said recesses in said punch supporting ring having a cylindrical surface for slidably supporting said punches for axial movement irrespective of rotation.

Z. A device as defined in claim 1 in which the contour of the grooves in said punch walls creates a relatively sharp corner where the groove wall meets the wall of the punch.

3. A device as defined in claim 1 in which the contour of the grooves in said punches is curved such that a tangent to the curve adjacent the surface of the punch is substantially normal to the surface of the punch.

4. A device as defined in claim 1 in which the punch is provided with a plurality of helical grooves disposed at opposite directions on the surface of each punch.

5. In a tablet press of the type having opposed, vertically-movable, circular die punches operating in opposed cylindrical recesses and movable from an axially a spaced position to a tablet compressing position for compressing powder in moving die pockets of a die plate, cam means extending along the path of said die punches, having cam grooves, circular cam follower means on each punch trackable in said cam grooves wherein said punches are free to rotate while being shifted axially to and from tablet compressing positions, said punches having helical grooves formed in the walls thereof extending axially beyond the length of said recesses whereby travel of said punches axially will expose each end of said grooves at the opposite ends of said recesses.

6. A device as defined in claim 5 in which the contourv of the grooves in said punch walls creates a relatively sharp corner where the groove wall meets the wall of the punch.

References Cited by the Examiner UNITED STATES PATENTS 857,043 6/1907 Endemann 107l8 2,539,674 10/1944 Pollock 107-17 WALTER A. SCHEEL, Primary Examiner.

10 ROBERT E. PULFREY, Examiner.

JOSEPH SHEA, Assistant Examiner. 

1. IN A TABLET PRESS OF THE TYPE HAVING OPPOSED VERTICALLY MOVABLE DIE PUNCHES EACH SLIDABLY MOUNTED IN A BEARING RECESS OF A PUNCH SUPPORTING RING FOR COMPRESSING POWDER IN A DIE OPENING, A CONSTRUCTION FOR PREVENTING THE ACCUMULATION OF POWDER ON THE BEARING SURFACES OF EACH PUNCH WITHIN SAID RECESS WHICH COMPRISES A PERIPHERAL WALL ON EACH PUNCH HAVING A HELICAL GROOVE EXTENDING LONGITUDINALLY OF THE PUNCH TO END PORTIONS THEREOF SO THAT AT THE EXTREMES OF THE STROKE OF THE PUNCH THE GROOVE WILL PROJECT FROM EACH END OF A PUNCH BEARING RECESS, SAID RECESSES IN SAID PUNCH SUPPORTING RING HAVING A CYLINDRICAL SURFACE FOR SLIDABLY SUPPORTING SAID PUNCHES FOR AXIAL MOVEMENT IRRESPECTIVE OF ROTATION. 